It is well known that semiconductor devices fabricated from SiC are in principle able to withstand high voltages in the blocking state of the device due to the fact that SiC has a very high breakdown field, approximately ten times higher than for Si. However, the devices have to be passivated by an insulating layer, which may be for instance SiO.sub.2, and devices having an insulated gate also have an insulating layer, which may also be for instance SiO.sub.2. In known devices the presence of such insulating layers places significant restrictions uses of the high breakdown field strength that would otherwise be possible for Sic-devices considering the properties of Sic itself. For instance in the case of insulating layers of SiO.sub.2, the dielectric constant in SiO.sub.2 is lower than in SiC, which means that the electric field will be higher in SiO.sub.2 according to the inverse ratio of the dielectric constant. A low field in the SiO.sub.2 layer is, however, beneficial to the long term stability and reliability of the insulating layer. At the maximum field strength of SiC (2 MV/cm) the corresponding field in SiO.sub.2 would be &gt;5 MV/cm which is generally considered as too high for stable device operation. Accordingly, it is necessary for protecting the insulating layer to restrict the maximum electric field in the SiC layers close to the insulating layers to a much lower level than SiC allows according to the dielectric strength of the oxide.
Accordingly, it is desirable to construct semiconductor devices of SiC in which the insulating layers are protected so utilize as much as possible the property capable to hold high voltages in the blocking state. It will then be particularly important to protect an insulating layer of a gate, since this will be much thinner than a passivation layer and the electric field will therefore be higher.